In general, various transportation means, carrying means and the like are used when cargo is loaded in or carried out from distribution warehouse, factory and the like and various auxiliary means such as the dock leveler is used for conforming a height of a deck of the distribution warehouse or factory to a height of a loading box of the transportation means such as cargo vehicle in order to stably carry and load the cargo from such a transportation means or carrying means.
As illustrated in FIG. 1, a prior dock leveler (1) is installed in an upper portion of an installation space (H) formed in a dock (D) of a warehouse or factory in such way that the height of the leveler can be adjusted. This dock leveler (1) is positioned at the same level as that of a plane of the dock (D) in a normal state, and has a plate (2) that can be raised or lowered depending to the height of a loading box of a transportation means at the time of carrying and loading of cargo or goods. A connecting plate (3) for connecting with the loading box of the transportation means is provided in such a way as to be developed at a front end portion of the plate (2). Furthermore, installed below the plate (2) is one or a plurality of lifting device (4) for practically lifting the plate (2) in a rotation manner. The lifting device (4) is generally formed of hydraulic cylinder or pneumatic cylinder etc., and an actuator (5) for supplying hydraulic pressure or pneumatic pressure is naturally connected to each lifting device (4), and a controller (6) for controlling each lifting device (4) and finally the lifting of the plate (2) is connected to the actuator (5).
According to the construction as described above, when the cargo is loaded on the transportation means or unloaded therefrom, if the controller (6) operates the actuator (5) depending on the height of the loading box of the transportation means, the hydraulic pressure or pneumatic pressure is supplied from the actuator (5) to the lifting device (4) or discharged from the lifting device (4) and accordingly the lifting device (4) is operated, whereby the plate (2) is raised or lowered, with a result of its height being adjusted. If the height of the plate (2) is adjusted as described above, the connecting plate (3) provided at the front end portion of the plate (2) is developed to be connected to the loading box of the transportation means, whereby the cargo can be stably carried out and loaded.
However, the prior dock leveler as described above is only used to carry out and load the cargo by simply conforming the level of the deck of the warehouse or factory to that of the loading box of the transportation means with use of the plate, and even though the height of the plate is decreased to the lowest level, a level difference with the ground occurs, and moreover even in the case when the plate is constructed to contact with the ground, it exhibits a steep inclination, and hence the transportation apparatus or carrying apparatus cannot pass through the plate, as a result there is a problem of applicability being limited.
Furthermore, there is another problem that, since installation of the actuators and lifting device is essential for raising and lowering the plate, installation and maintenance costs are excessively spent.